1. Field of the Invention
The present invention relates to a method and apparatus for controlling the fuel supply of an internal combustion engine in response to engine operating parameters.
2. Description of the Prior Art
In one known fuel supply control method, the engine running speed and the intake manifold pneumatic pressure are detected, and then used to calculate the basic pulse width of an injection signal to be applied to the fuel injectors. This basic pulse width is corrected in accordance with the engine temperature such as the coolant temperature. The corrected injection pulse width is used to adjust the actual fuel supply.
It is accepted practice to correct the increment of injection pulse width (correction of warming-up increment) depending upon the engine temperature in order to improve the operating performance of the engine when it is cold. Immediately after the engine starts to run, however, such a correction of warming-up increment is not sufficient; i.e., more of an increment of fuel is necessary for obtaining stabilized operation of the engine immediately after the engine is started. Namely, immediately after starting, the lubricating oil is so cold that the lubricating function is not fully exhibited. Furthermore, the wall temperature of the combustion chamber is so low that the gas does not completely burn. In order to stably run the engine therefore, a correction of fuel increment after starting, which increases fuel more than during warming-up is necessary. According to the conventional fuel supply control method, the amount of fuel supply is increased for a fixed period of time after engine starting. According to such a conventional method, therefore, the amount of fuel supplied after engine starting cannot be controlled to an ideal increment or an ideal period of increment required for the engine. When the engine condition changes to a heavy-load condition immediately after starting, the engine temperature rises quickly, and thus the amount of fuel supplied need be increased for a short period of time after starting. When the engine is maintained under the idling condition after starting, on the other hand, since the engine temperature rises slowly, the amount of fuel supplied should be increased for an extended period of time after starting.
Furthermore, if the above-mentioned fuel increment after starting is always carried out after the engine starts, an air-fuel ratio of mixture supplied to the engine sometimes becomes too rich with respect to a stoichiometric condition. There is no problem when the engine starts from the cold condition. However, in the case that the engine is started again after being warmed-up, if the fuel increment after starting is carried out, the air-fuel ratio is extremely enriched causing the exhaust emission characteristics to extremely deteriorate and causing fuel consumption to unefficiently increase.